The invention is directed to a method for the low-maintenance operation of an apparatus for producing surface structures on a roller with an electron beam, whereby the electron beam is charged by a focusing for variation of its bundling and whereby the apparatus is composed of a vacuum chamber for the acceptance of the roller as well as of a beam equipment that generates the electron beam, said beam equipment comprising a passage for the electron beam in a wall that separates the beam equipment from the vacuum chamber.
Over and above this, the invention is directed to an apparatus for the implementation of the method, said apparatus being composed of a beam equipment having a beam generator that generates the electron beam, of a focal length adjustment as well as having a focusing, and of a vacuum chamber that accepts the roller, whereby the beam equipment comprises a passage for the electron beam in a wall that separates the beam equipment from the vacuum chamber.
Different methods have been applied for producing such rollers that, for example, are fashioned as textured rollers or dressing rollers and are particularly employed for producing a surface structure on sheet steel. On the one hand, particle charging with steel grit corresponding to a shot hole has been carried out; on the other hand, depressions were produced on the roller by electro-erosion or by processing with a laser. Electro-erosion or particle charging with steel grit, however, leads to recesses or depressions limited by sharp edges whose edge regions tend to break off and, thus, to develop dust. In electro-erosion and in laser charging, an oxidation of the roller metal and, thus, a formation of ash also can occur. The plurality of depressions to be produced on the roller surface also is limited by the inertia of the mirrors employed when processing with lasers.
In the manufacture of printing cylinders for rotogravure, depressions or cups that accept the inks during later printing are produced on the roller surface with the assistance of the electron beam. Crater walls potentially arising in the production of the depressions are eroded after the conclusion of the cylinder engraving.
DE-AS 28 40 702 discloses a method and an apparatus for improving the quality of fine steel sheets. It is recited in this publication that a surface structure on the roller surface ensues with the assistance of an intermittent energy beam along a helical path. It is particularly cited that a laser beam can be employed as the energy beam. However, it is also pointed out that an electron beam can be employed. Specific references to description of the implementation of a method upon employment of an electron beam or for constructing an apparatus that applies this method are not recited.
EP-A-0 119 182 discloses that a roller surface can be charged with the assistance of a laser beam or an electron beam. A helical path on the roller surface is produced with the assistance of the beam. In particular, it discussed how to blow a gas, for example oxygen, into the region of the beam charging. As a result of the presence of oxygen, an oxidation of the roller metal ensues in the region of the beam charging. The formation of a crater wall that surrounds a recess produced by the beam is thereby largely avoided, since the material that evaporates or that is hurled from the recess in its molten condition reacts very quickly with the oxygen.
EP-B-0 108 376 discloses that the engraving of printing cylinders be implemented with the assistance of an electron beam charging and to guarantee an after-engraving relative to an engraving that has already ensued on the basis of a special single-phase procedure. The topical arrangement of the recesses on the printing cylinder produced with the assistance of the apparatus disclosed in this publication is prescribed by the printing format that is to be produced.
As discussed therein, the particles stripped from the roller material in the production of the recesses on the roller surface are at least partly evaporated due to the high temperatures prevailing in the region of the electron beam charging. After cooling, a major part of this vapor precipitates in a vacuum chamber that accepts the roller. A more highly pronounced vacuum usually prevails in the region of the beam equipment than in the region of the vacuum chamber. This leads to the fact that evaporated material particles can penetrate into the region of the beam equipment.
The majority of these penetrating material particles precipitate in the region of a passage that is arranged within a wall separating the beam equipment from the vacuum chamber and that enables a transfer of the electron beam from the beam equipment into the vacuum chamber. Particularly given an interaction with a cooling that tempers the wall in the region of the passage, one must count on the passage growing shut. When engraving a steel roller, a few cubic centimeters of metal are evaporated and the region of the passage can grow shut within a time span of approximately 30 through 60 minutes due to this considerable number of material particles. The exact positioning of the electron beam can be deteriorated before the passage completely grows shut. Over and above this, one must count on a considerable, local temperature rise given a permanent incidence of the electron on the regions growing shut, this potentially leading to damage to the apparatus. In order to avoid these disadvantages, a frequent replacement of an insert arranged in the region of the passage or, respectively, a frequent cleaning of the passage were required in the past. These maintenance jobs require a not insubstantial work outlay and involve interruptions in production.